The present invention relates to the production of maleic anhydride from normal butane.
Prior processes for the conversion of butane to maleic anhydride include, for example, Bergman et al., U.S. Pat. No. 3,293,268 "Production of Maleic Anhydride by Oxidation of n-Butane." According to Bergman et al., the oxidation of normal butane is carried out by contacting the normal butane with oxygen gas and a phosphorus vanadium oxide catalyst at a temperature between 500.degree. and 600.degree. C (932.degree. to 1,112.degree. F). To assure maintaining the temperature within about 932.degree. to 1,112.degree. F in the catalyst-filled reactor tubes, Bergman et al. suggest using a molten salt bath mixture. Such a molten salt bath circulates outside the tubes, that is, on the shell side of a shell and tube heat exchanger type configuration with the catalyst located inside the tubes. See further in this regard Frank, U.S. Pat. No. 3,904,652.
Schneider, U.S. Pat. No. 3,864,280 also discloses oxidation of normal butane to maleic anhydride using a catalyst comprising vanadium and phosphorus oxides.
Prior to Bergman et al. and Schneider, little disclosure had been made of catalytic processes for oxidation of normal butane to maleic anhydride. Thus, as pointed out in the Bergman et al. patent, various oxidation catalysts had been used for oxidation of benzene or butene to maleic anhydride, but generally not for oxidation of normal butane because relatively poor yields of maleic anhydride were obtained when normal butane was used as the feedstock. See also in this regard, U.S. Pat. No. 2,691,606 indicating that benzene and butene were commercially exploited as feedstocks rather than paraffins such as normal butane because it had been found more difficult to oxidize normal butane to maleic anhydride.
The pressure typically used in prior art processes was that sufficient to drive the product gas stream through a water scrubber, about 1 to 5 psig.
Brown et al., Proc. Roy. Soc., Ser. A, 326, 215-227 (1972) disclosed oxidation of benzene to maleic anhydride with further reaction taking place in the catalyst bed and in free space after the catalyst bed at a temperature of 779.degree. F.